Extract names from vector according to their values
On Aug 2, 2011, at 2:21 PM, Sverre Stausland wrote:
Dear helpers, I can create a vector with the priority of the packages that came with R, like this:
installed.packages()[,"Priority"]->my.vector my.vector
base boot class cluster codetools
"base" "recommended" "recommended" "recommended" "recommended"
compiler datasets foreign graphics grDevices
"base" "base" "recommended" "base" "base"
grid KernSmooth lattice MASS Matrix
"base" "recommended" "recommended" "recommended" "recommended"
methods mgcv nlme nnet rpart
"base" "recommended" "recommended" "recommended" "recommended"
spatial splines stats stats4 survival
"recommended" "base" "base" "base" "recommended"
tcltk tools utils
"base" "base" "base"
How can I extract the names from this vector according to their
priority? I.e. I want to create a vector from this with the names of
the "base" packages, and another vector with the names of the
"recommended" packages.
> names( my.vector[which(my.vector=="recommended")]) [1] "boot" "class" "cluster" [4] "codetools" "foreign" "KernSmooth" [7] "lattice" "MASS" "Matrix" [10] "mgcv" "nlme" "nnet" [13] "rpart" "spatial" "survival" Note that some people may tell you that this form below should be preferred because the 'which' is superfluous. It is not. The "[" function returns all the NA's fr reasons that are unclear to me. It is wiser to use `which` so that you get numerical indexing. > names(my.vector[my.vector=="recommended"]) On my system it produces 493 items most of them NA's.
David Winsemius, MD West Hartford, CT